Method for manufacturing reflective structure

ABSTRACT

A method for manufacturing reflective structure is provided. The method includes the operations as follows. A metallization structure is received. A plurality of conductive pads are formed over the metallization structure. A plurality of dielectric stacks are formed over the conductive pads, respectively, wherein the thicknesses of the dielectric stacks are different. The dielectric stacks are isolated by forming a plurality of trenches over a plurality of intervals between each two adjacent dielectric stacks.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of prior-filed U.S.application Ser. No. 16/732,222, filed 31 December, 2019, and claims thepriority thereto.

FIELD

The present disclosure is related to a semiconductor structure and, moreparticularly, to a semiconductor structure having a reflective structurewith ascending refractive index.

BACKGROUND

Light-emitting diodes (LED) are considered playing an important roleamong the display technologies for the next-generation. The chip for LEDdisplay bears similar features to those currently in use for generallighting, but its size is shrunk to below 200 microns. In theory,micro-LED displays may make LED structures thinner, smaller, and in anarray structure. The size of individual micro-LED usually ranges from 1to 10 μm. In general, the advantages of high efficiency and long lifespan of conventional LED chips are inherited by miniaturized ones, andas the size gets smaller, the resolution may be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various structures are not drawn to scale. In fact, the dimensions ofthe various structures may be arbitrarily increased or reduced forclarity of discussion.

FIG. 1 illustrates a cross-sectional view of a reflective structureaccording to some embodiments of the present disclosure.

FIG. 2 illustrates a line chart regarding the reflectivity and therefractive index of the second dielectric film according to someembodiments of the present disclosure.

FIG. 3 illustrates a cross-sectional view of a reflective structureaccording to some embodiments of the present disclosure.

FIG. 4 illustrates a line chart regarding the total reflectivity and thedielectric film counts according to some embodiments of the presentdisclosure.

FIG. 5 illustrates a cross-sectional view of a reflective structureaccording to some embodiments of the present disclosure.

FIGS. 6A, 6B, 6C, 6D, 6E, 6Ea, 6F, 6Fa, 6G, 6H and 6I illustratecross-sectional views at various operations of manufacturing asemiconductor structure according to some embodiments of the presentdisclosure.

FIG. 7A illustrates a scatter gram regarding the total reflectivity ofthe reflective structure according to some embodiments of the presentdisclosure.

FIG. 7B illustrates a scatter gram regarding the total reflectivity ofthe reflective structure according to some embodiments of the presentdisclosure.

FIG. 7C illustrates a scatter gram regarding the total reflectivity ofthe reflective structure according to some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of elements and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper”, “on” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the terms such as “first”, “second” and “third” describevarious elements, components, regions, layers and/or sections, theseelements, components, regions, layers and/or sections should not belimited by these terms. These terms may be only used to distinguish oneelement, component, region, layer or section from another. The termssuch as “first”, “second”, and “third” when used herein do not imply asequence or order unless clearly indicated by the context.

The reflectivity is the ratio of reflected optical power to the incidentoptical power at a flat surface of an object. It can be influenced byseveral physical properties of the reflecting object such as the type ofsurface materials, surface roughness, thickness, uniformity, flatness,geometric structure of the object, etc. For example, the higher of theuniformity of the surface material, the higher of reflectivity may bepresented.

As shown in FIG. 1, in some embodiments, the reflective structure 1 ofthe present disclosure includes a metal base 10 and a dielectric layer20. The metal base 10 has a first surface 101. The dielectric layer 20includes a first dielectric film 201, a second dielectric film 202, anda third dielectric film 203.

The metal base 10 may be a conductive pad and may be made by anysuitable conductive material includes but not limited to metal (e.g.,copper, tantalum, titanium, molybdenum, tungsten, platinum, aluminum,hafnium, ruthenium), alloy, metal silicide (e.g., titanium silicide,cobalt silicide, nickel silicide, tantalum silicide), or metal nitride(e.g., titanium nitride, tantalum nitride). In some embodiments, themetal base is made by aluminum copper. In some embodiments, the metalbase 10 is formed by chemical vapor deposition (CVD), low pressurechemical vapor deposition, physical vapor deposition (PVD), atomic layerdeposition, or spin-on.

The dielectric layer 20 is disposed on the first surface 101 of themetal base 10, and accordingly, the first dielectric film 201, thesecond dielectric film 202, and the third dielectric film 203 arestacked over the metal base 10. The dielectric layer 20 on the metalbase 10 is configured to reflect lights with the metal base 10. Moreprecisely, an incident ray shined on the metal base 10 may firstlytravel through the third dielectric film 203, the second dielectric film202, and the first dielectric film 201 sequentially before beingreflected by the first surface 101 of the metal base 10, and thereflected ray may then travel back reversely.

Because the dielectric layer 20 is not composed of a single film, theincident ray and reflected ray traveled therein may be influenced underSnell's Law. That is, while the ray travels from one medium to another,for instance, from the third dielectric film 203 to the seconddielectric film 202, the ray may be refracted if the refractive indexesthereof are different. According to Snell's Law, when n1 and n2represent the refractive indexes for the two media, and θ1 and θ2 arethe angles of incidence and refraction that the ray makes with theperpendicular line at the boundary. Snell's law asserts that n1/n2=sinθ1/sin θ2.

In some embodiments, a refractive index of the first dielectric film 201is smaller than a refractive index of the second dielectric film 202,and the refractive index of the second dielectric film 202 is smallerthan a refractive index of the third dielectric film 203. In otherwords, the refractive index of a dielectric film proximity to the metalbase 10 are smaller than the refractive indexes of a dielectric filmdistance to the metal base 10. In some embodiments, the refractiveindexes of the dielectric films from the bottom of the dielectric layer20 to the top of the dielectric layer 20 are changed in an ascendingorder.

In the present disclosure, the refractive indexes ascending from thebottom of the dielectric layer to the top of the dielectric layer mayincrease the total reflectivity of light of the reflective structure. Insome embodiments, the refractive indexes of the dielectric films of thedielectric layer 20 are in a range about 1.47 to about 1.8. In someembodiments, the refractive indexes of the first dielectric film 201 andthe third dielectric film 203 are 1.47 and 1.8, respectively, while therefractive index of the second dielectric film 202 is at some pointbetween 1.47 and 1.8, which is different to the first dielectric film201 and the third dielectric film 203.

Referring to FIG. 2, FIG. 2 illustrates a relation between totalreflectivity (Y axis) of the dielectric layer 20 with respect to thechange of the refractive index (X axis) of the second dielectric film202 of the dielectric layer 20. The total reflectivity of light shows atrend of increase when the refractive index of the second dielectricfilm 202 is increased. Comparing between the reflectivity of the redlight (with wavelength at about 633 nm, labeled as square dots) in theexamples R1 and R2, when the refractive indexes of the first dielectricfilm 201 and the second dielectric film 202 are identical, asdemonstrated in the example R1, a total reflectivity of about 88.6% islower than a total reflectivity of about 91.7% of R2, in which therefractive index of the first dielectric film 201 is lower than that ofthe second dielectric film 202. Alternatively, by changing therefractive index of the second dielectric film 202 from identical togreater than that of the first dielectric film 201, the reflectivity ofthe red light in the dielectric layer 20 may be increased from 88.6% to91.7%, with refractive index of the third dielectric film 203 unchanged.

Moreover, as shown in FIG. 2, not only the red light, but also the totalreflectivity of the green light (with wavelength at about 500 nm,labeled as triangle dots) and the total reflectivity of the blue light(with wavelength at about 450 nm, labeled as diamond dots) are allincreased as the increasing of the refractive index of the seconddielectric film 202. In other words, in the wavelength range of visiblelight, the total reflectivity may be increased if the refractive indexof the second dielectric film 202, or the middle layer of the dielectricfilm 202, is between the refractive index range of the first dielectricfilm 201 and the third dielectric film 203.

Also, according to FIG. 2, the total reflectivity of light shows apositive correlation with the refractive index of the second dielectricfilm 202. For example, in the case of the refractive indexes of thefirst dielectric film 201 and the third dielectric film 203 are 1.47 and1.8, respectively, the increase of the total reflectivity of light ismore prominent when the refractive index of the second dielectric film202 is increased from 1.47 to 1.75, as opposed to being increased from1.47 to 1.5. In some embodiments, the total reflectivity of light may befurther increased if the refractive index of the second dielectric film202 is higher than an average of the refractive indexes of the firstdielectric film 201 and the third dielectric film 203. That is, when therefractive index of the first dielectric film 201 is about 1.47, and therefractive index of the third dielectric film 203 is about 1.8, thetotal reflectivity of light may be further increased if the refractiveindex of the second dielectric film 202 is greater than 1.63.

By increasing the total reflectivity of the light through arranging theorder of the dielectric films, the requirement regarding the uniformityof the dielectric layer 20 may be alleviated. More precisely, in orderto reach high reflectivity, the formation of the dielectric layer on areflective metal is required to have a rigorous planarization process tomeet a surface roughness uniformity of <1% (3 sigma). However, suchrequirement regarding the uniformity may be alleviated because theascending order of the refractive indexes of the dielectric films mayprovide, for instance, an increase of total reflectivity more than 3% asshown in FIG. 2. Accordingly, it would be more flexible in manufacturingreflectors in semiconductor structures.

Referring to FIG. 3, in some embodiments, the dielectric layer 20 mayinclude more than three dielectric films. In some embodiments, thesecond dielectric film 202 may include a plurality of sublayers, forexample, the sublayers 202A, 202B, and 202C as shown in FIG. 3. In someembodiments, the sublayers 202A, 202B, and 202C are disposed between thefirst dielectric film 201 and the third dielectric film 203. In suchembodiments, the refractive indexes of the sublayers 202A, 202B, and202C are arranged in an order that the sublayers closer to the thirddielectric film 203 has higher refractive indexes, that is, therefractive index of a bottom sublayer of the second dielectric film 202(e.g. sublayer 202A) is smaller than the refractive index of a topsublayer of the second dielectric film 202 (e.g. sublayer 202C).

The counts of the sublayers of the second dielectric film 202 are notlimited to the sublayers as shown in FIG. 3. Referring to FIG. 4, FIG. 4shows a relation of the total reflectivity with respect to thedielectric film counts. When the second dielectric film 202 includesfour sublayers, as previously discussed in FIG. 3, in addition to thefirst dielectric film 201 and the third dielectric film 203, thedielectric layer 20 possess a film counts of six dielectric films. Thetotal reflectivity of light is still higher than that of a reflectorwith only one or two dielectric films. In other words, in the case ofthe dielectric layer 20 having a dielectric film counts of three, totalreflectivity substantially saturates its performance even if the filmcounts go up. Considering FIG. 2 and FIG. 4, with an ascendingrefractive index from the first dielectric film 201 to the thirddielectric film 203, or a middle film thereof further includes amulti-sublayer structure with an ascending refractive index, the totalreflectivity of light may be increased in such dielectric filmarrangement. In some embodiments, the refractive indexes of theplurality of sublayers are in a range of from about 1.47 to about 1.8.

In some embodiments, the material of the first dielectric film 201 isidentical with the material of the second dielectric film 202. In someembodiments, the material of the first dielectric film 201 is siliconoxide. In some embodiments, although the materials of the firstdielectric film 201 and the second dielectric film 202 are identical,the refractive indexes of the first dielectric film 201 and the seconddielectric film 202 are still different by selecting differentprecursors or adjusting the ratio of the precursor during the formingoperation of the dielectric films.

In some embodiments, the material of the first dielectric film 201 isdifferent from the material of the third dielectric film 203. In someembodiments, the material of the third dielectric film 203 is aluminumoxide.

In some embodiments, each of the materials of the first dielectric film201, the second dielectric film 202, and the third dielectric film 203has an extinction coefficient (k) substantially equal to zero so thatthe light passing through may not be substantially attenuated.

Referring to FIG. 5, in some embodiments, a conductive oxide layer 40 isdisposed over the dielectric layer 20, and a conductive pad 30 isdisposed below the dielectric layer 20. The material and the formingmethod of the conductive pad 30 may refer to the previously describedmetal base in FIG. 1. In some embodiments, the conductive pad 30 islaterally surrounded by an insulating layer 31. In some embodiments, atop surface 310 of the insulating layer 31 is coplanar with a topsurface 300 of the conductive pad 30.

Moreover, in some embodiments, the dielectric layer 20 includes a raisedportion 21 and at least an edge portion 22 at a side of the dielectriclayer 20. As shown in FIG. 5, the thickness of the dielectric layer 20is varied in different portions.

The thickness of the dielectric layer 20, particularly, the thickness T1of the raised portion 21 is associated with the color of the reflectedray reflected by the present disclosure. More precisely, the color ofthe reflected ray is determined by the thickness of the dielectric layer20, because portions of the wavelength of the incident ray shined on thetop surface 300 of the conductive pad 30 may be absorbed depends on thethickness of the dielectric layer 20 and only other portions of thewavelength of the incident ray may be reflected. In some embodiments,the light with a wavelength at about 630 nm to about 750 nm may bereflected by the reflective structure with a thickness of the dielectriclayer 20 at about 1500 angstroms and thereby be observed as red light.In some embodiments, the light with a wavelength at about 490 nm toabout 570 nm may be reflected by the reflective structure with athickness of the dielectric layer 20 at about 700 angstroms and therebybe observed as green light. In some embodiments, the light with awavelength at about 450 nm to about 490 nm may be reflected by thereflective structure with a thickness of the dielectric layer 20 atabout 50 angstroms and thereby be observed as blue light. In otherwords, with the decreasing of the thickness of dielectric layer 20, thewavelength of the reflected ray is also decreased and beyond the rangeof visible light eventually.

Furthermore, the thickness T2 of the edge portion 22 is smaller than thethickness T1 of the raised portion 21, whereas in some embodiments, theedge portion 22 is the area that not for reflecting visible light.Therefore, in some embodiments, the thickness T2 of the edge portion 22is smaller than about 50 angstroms and no visible light may besubstantially reflected at the edge portion 22.

Still referring to FIG. 5, in some embodiments, the conductive pad 30 isentirely covered by the raised portion 21. In some embodiments, not onlythe conductive pad 30, but also a portion of the insulating layer 31 iscovered by the raised portion 21. For instance, according to thesectional view in FIG. 5, the raised portion 21 may be wider than theconductive pad 30 with a width W at each side of the raised portion 21.Therefore, some oblique incident rays may also travel through the raisedportion 21 and be reflected. In some embodiments, the area of the raisedportion 21 is greater than the area of the conductive pad 30 therebelow. In some embodiment, FIG. 5 shows a portion of a pixel in a lightemitting device adjacent to its light-receiving side.

Referring to FIGS. 6A to 6H, in manufacturing a semiconductor structurewith a reflective structure, in some embodiments, a metallizationstructure 50 may be firstly provided. As shown in FIG. 6A, themetallization structure 50 includes a plurality of individual devicessuch as transistors, capacitors, and resistors patterned in a substrate501 (e.g. silicon wafer) by formation operations of front end of line(FEOL). And a series of stacked layers 502 are disposed over thesubstrate 501 by formation operations of back end of line (BEOL). Thestacked layers are fabricated to provide individual devices such asabove mentioned transistors, capacitors, and resistors to getinterconnected with metal wiring on the substrate. Accordingly, adjacentlayers 502 in the metallization structure 50 are linked together throughthe use of electrical contacts and vias.

As shown in FIG. 6B, in some embodiments, a plurality of conductive pads30 are disposed over the metallization structure 50. In someembodiments, the plurality of conductive pads 30 are laterallysurrounded by an insulating layer 31, and a top surface 310 of theinsulating layer 31 is coplanar with a plurality of top surfaces 300 ofthe conductive pads 30. In some embodiments, the conductive pads 30 maybe made by any suitable conductive material includes but not limited tometal, alloy, metal silicide, or metal nitride. In some embodiments, theconductive pads 30 are made by aluminum copper (AlCu). In someembodiments, the conductive pads 30 is formed by chemical vapordeposition (CVD), low pressure chemical vapor deposition, physical vapordeposition (PVD), atomic layer deposition (ALD), or spin-on.

Before forming the dielectric layer over the conductive pads 30, in someembodiments, the conductive pads 30 made by aluminum copper may beannealed at about 400 Celsius degrees for about 1 minute. The annealingoperation is to induce the growth of the hillocks or extrusions form theconductive pads 30 before the depositing operation of the dielectriclayer. The hillocks or extrusions may be removed by a followed chemicalmechanical planarization (CMP) operation.

As shown in FIGS. 6C to 6E, after the CMP operation implemented to theconductive pads 30, the dielectric layer 20 is disposed on theconductive pads 30. In some embodiments, the operation temperature informing the dielectric layer 20 is lower than the annealing operation ofthe conductive pads 30. In some embodiments, the dielectric layer 20 isformed by plasma enhanced physical vapor deposition (PECVD) at about 250Celsius degrees. The lower temperature in forming the dielectric layer20 may maintain a lower surface roughness of the conductive pads 30,that is, the growth of the hillocks or extrusions may be avoided if thetemperature in forming the dielectric layer 20 is not as high as that inthe previous annealing operation.

In some embodiments, the surface roughness of the conductive pads 30made by aluminum copper may be decreased from less than about 350angstroms to less than about 250 angstroms by annealing the conductivepads 30 at about 400 Celsius degrees for about 1 minute. In someembodiments, the surface roughness of the conductive pads 30 made byaluminum copper may be further decreased from less than about 250angstroms to less than about 100 angstroms by lowering the PECVDtemperature in forming the dielectric layer 20 from about 400 Celsiusdegrees to about 250 Celsius degrees.

In some embodiments, the dielectric layer 20 is formed by a plurality ofdeposition operations, depending on the counts of the dielectric filmsand the distribution requirement of colors in a pixel unit. Referring toFIGS. 6C to 6E, in order to form the reflective structure which hasdifferent thickness for reflecting different colors of light, in someembodiments, the forming of the dielectric films over the firstconductive pad 30A, the second conductive pad 30B, and the thirdconductive pad 30C may be divided into three different areas 61, 62, and63 through three masking operations. In some embodiments, the threedifferent areas 61, 62, and 63 may be three pixels configured to reflectdifferent wavelengths, and the three different areas 61, 62, and 63 maybe adjacent or not adjacent to each other in a pixel array.

In some embodiments, as shown in FIG. 6C, the area 61 over the firstconductive pad 30A is for reflecting red light and the total thicknessof the dielectric layer 20 therein is about 1500 angstroms. Thethickness of the first dielectric film 201, the second dielectric film202, and the third dielectric film 203, for instance, may be about 725,725, and 50 angstroms, respectively. The different dielectric films withascending refractive indexes may be formed by selecting differentprecursors or adjusting the ratio of the precursor during a firstmasking operation.

In some embodiments, as shown in FIG. 6D, the area 62 over the secondconductive pad 30B is for reflecting green light and the total thicknessof the dielectric layer 20 therein is about 700 angstroms. The thicknessof the first dielectric film 201, the second dielectric film 202, andthe third dielectric film 203, for instance, may be about 330, 330, and40 angstroms, respectively. The different dielectric films withascending refractive indexes may be formed by selecting differentprecursors or adjusting the ratio of the precursor during a secondmasking operation.

In some embodiments, as shown in FIG. 6E, the area 63 over the thirdconductive pad 30C is for reflecting green light and the total thicknessof the dielectric layer 20 therein is about 50 angstroms. The thicknessof the first dielectric film 201, the second dielectric film 202, andthe third dielectric film 203, for instance, may be about 20, 20, and 10angstroms, respectively. The different dielectric films with ascendingrefractive indexes may be formed by selecting different precursors oradjusting the ratio of the precursor during a third masking operation.

Consequently, in the areas 61, 62, and 63, the thicknesses of thedielectric layer 20 are about 1500, 700, and 50 angstroms, respectively,and each area also includes the first dielectric film 201, the seconddielectric film 202, and the third dielectric film 203 with therefractive index, for instance, 1.47, 1.7, and 1.8, respectively, whichis ascending from the bottom film of the dielectric layer 20 to the topfilm thereof. More precisely, as shown in FIG. 6Ea, which is enlargedfrom a portion of FIG. 6E, the first conductive pad 30A and the secondconductive pad 30B are disposed over the metallization structure 50. Thefirst dielectric film 201 has a first thickness T61 on the firstconductive pad 30A and a second thickness T62 on the second conductivepad 30B, and the first thickness is different from the second thicknessT62. The second dielectric film 202 has third thickness T63 over thefirst conductive pad 30A and a fourth thickness T64 over the secondconductive pad 30B, and the third thickness T63 is different from thefourth thickness T64. The third dielectric film 203 has a fifththickness T65 over the first conductive pad 30A and a sixth thicknessT66 over the second conductive pad 30B, and the fifth thickness T65 isdifferent from the sixth thickness T66.

As shown in FIG. 6F, in some embodiments, the dielectric layer 20includes a plurality of recesses 64 over a plurality of intervals 32between each two adjacent conductive pads 30. In some embodiments, therecesses 64 may be formed by etching operations. The recesses 64 mayisolate the areas 61, 62, and 63 mentioned in previous operations intothe raised portions 21 and the edge portions 22 as previously mentionedin FIG. 5. In some embodiments, the thickness of the dielectric layer 20at the bottom of the recesses 64 is smaller than about 50 angstroms andthus no visible light may be substantially reflected.

In some embodiments, the method for forming the dielectric films is notlimited to PECVD, for example, the first dielectric film 201 and thesecond dielectric film 202 may be formed by CVD or PECVD, whereas thethird dielectric film 203 is formed by ALD. Particularly, in someembodiments, the material of the first dielectric film 201 and thesecond dielectric film 202 are silicon oxide instead of aluminum oxideused in the third dielectric film 203. Accordingly, in some embodiments,a density of the first dielectric firm 201 or the second dielectric film202 is smaller than a density of the third dielectric film 203.

As shown in FIG. 6Fa, according to a top view of the semiconductorstructure formed by the operations as shown in FIGS. 6A to 6F, theraised portions 21R, 21G, and 21B of the dielectric layer may reflectred light, green light, and blue light, respectively, and the raisedportions 21R, 21G, and 21B may be distinguished by the edge portion 22clearly.

As shown in FIG. 6G, in some embodiments, a plurality of electricalconnections 70 may be formed through each of the raised portions 21 ofthe dielectric layer 20 in a plurality of contact forming operations.And as shown in FIG. 6H, the conductive oxide layer 40 is formed overthe dielectric layer 20. More precisely, each of the raised portions 21may be covered by the conductive oxide layer 40, and the electricalconnections 70 may connect the conductive oxide layer 40 and theconductive pads 30. In some embodiments, the conductive oxide layer 40is an indium tin oxide (ITO) layer.

The reflective structure described herein may be integrated with lightemitting devices such as a micro-OLED 42. The dielectric layer 20 issurrounded by a subsequently-deposited insulating layer 41 to fill thegap between adjacent dielectric layers 20. The micro-OLED 42 can bedisposed over the insulating layer 41 and the reflective structure. Insome embodiments, the conductive oxide layer 40 is in contact with anelectrode of the micro-OLED 42. In some embodiments, as shown in FIG.6I, the lights L from the micro-OLED 42 enter the dielectric layer 20 ofthe reflective structure. More precisely, the lights L may penetrate thedielectric layers 20 and be reflected by the conductive pads 30. Asaforementioned, the thickness of the dielectric layer 20 is related tothe wavelength that the dielectric layers 20 reflected. In someembodiments, the Red light R, Green light G, and Blue light B may bereflected by the dielectric layers 20 with different thicknesses. Insome embodiments, the source of the light L may be light emitting layersdisposed higher than the reflective structure. For the purpose of cleardemonstration, differences among the thicknesses of each of thedielectric layers 20 are not drawn according to scale. Thicknessdifference between each of the dielectric layers 20 can bemicroscopically minute and hence the conductive oxide layers 40 on eachof the discrete dielectric layers 20 can be in contact with theelectrode of the micro-OLED 42.

Referring to FIG. 7A, FIG. 7A shows a relation between a totalreflectivity of the dielectric layer with respect to different incidentwavelengths. The total reflectivity of a reflective structure iscompared under two conditions: one by forming three dielectric filmswith ascending refractive indexes in an order of from conductive pad 30to the conductive oxide layer 40, another by forming three dielectricfilms with descending refractive indexes in an order of from conductivepad 30 to the conductive oxide layer 40. The line 81A refers to thetotal reflectivity that the dielectric films with refractive indexes ofabout 1.47, 1.7, and 1.8 stacked from the bottom to the top, whereaswith the refractive indexes of about 1.8, 1.7, and 1.47 stacked from thebottom to the top referred as the line SIB. In the wavelength of visiblelight (about 380 nm to 750 nm), the total reflectivity of the reflectivestructure with ascending refractive indexes is higher than that withdescending refractive indexes.

Referring to FIG. 7B, FIG. 7B shows a relation between a totalreflectivity of the dielectric layer with respect to different incidentwavelengths. The total reflectivity of a reflective structure iscompared under two conditions: one by forming four dielectric films withascending refractive indexes in an order of from conductive pad 30 tothe conductive oxide layer 40, another by forming four dielectric filmswith descending refractive indexes in an order of from conductive pad 30to the conductive oxide layer 40. The line 82A refers to the totalreflectivity that the dielectric films with refractive indexes of about1.5, 1.6, 1.7, and 1.8 stacked from the bottom to the top, whereas withthe refractive indexes of about 1.8, 1.7, 1.6 and 1.5 stacked from thebottom to the top referred as the line 82B. In the wavelength of visiblelight, the total reflectivity of the reflective structure with more thanthree ascending refractive indexes is also higher than that withdescending refractive indexes.

Referring to FIG. 7C, FIG. 7C shows a relation between a totalreflectivity of the dielectric layer with respect to different incidentwavelengths. The total reflectivity of a reflective structure iscompared under three conditions: one by forming three dielectric filmswith ascending refractive indexes in an order of from conductive pad 30to the conductive oxide layer 40, another by forming three dielectricfilms with descending refractive indexes in an order of from conductivepad 30 to the conductive oxide layer 40, yet another by forming threedielectric films with random refractive indexes arrangement other thanascending or descending order. The line 83A refers to the reflectivitythat the dielectric films with refractive indexes of about 1.47, 1.7,and 1.8 stacked from the bottom to the top, whereas with the refractiveindexes of about 1.8, 1.7, and 1.47 stacked from the bottom to the topreferred as the line 83B, and whereas with the refractive indexes ofabout 1.7, 1.8, and 1.47 stacked from the bottom to the top referred asthe line 83C. In the wavelength of visible light, the total reflectivityof the reflective structure with ascending refractive indexes is notonly higher than that with descending refractive indexes, but alsohigher than that with random refractive indexes.

In the present disclosure, the reflective structure includes adielectric layer on a metal base with at least three dielectric filmsstacked with refractive indexes arranged in an ascending order. Thetotal reflectivity of the reflective structure may thus be increased,and the requirement of uniformity of the dielectric layer may bealleviated.

In one exemplary aspect, a reflective structure is provided. Thereflective structure includes: a metal base and a dielectric layer. Themetal base has a first surface. The dielectric layer is disposed on thefirst surface, and has a first dielectric film, a second dielectricfilm, and a third dielectric film. The first dielectric film is disposedon the first surface. The second dielectric film is disposed on thefirst dielectric film. The third dielectric film is disposed on thesecond dielectric film. A refractive index of the first dielectric filmis smaller than a refractive index of the second dielectric film, andthe refractive index of the second dielectric film is smaller than arefractive index of the third dielectric film.

In another exemplary aspect, a reflective structure is provided. Thereflective structure includes: an interconnect structure, a first metalbase, a second metal base, a first dielectric film, a second dielectricfilm, and a third dielectric film. The first metal base and the secondmetal base are over the interconnect structure. The first dielectricfilm has a first thickness on the first metal base and a secondthickness on the second metal base. The first thickness is differentfrom the second thickness. The second dielectric film is on the firstdielectric film. The second dielectric film has a third thickness overthe first metal base and a fourth thickness over the second metal base.The third thickness is different from the fourth thickness. The thirddielectric film is on the second dielectric film. The third dielectricfilm has a fifth thickness over the first metal base and a sixththickness over the second metal base. The fifth thickness is differentfrom the sixth thickness. The refractive index of the first dielectricfilm is smaller than a refractive index of the second dielectric film,and the refractive index of the second dielectric film is smaller than arefractive index of the third dielectric film.

In yet another exemplary aspect, a semiconductor structure is provided.The semiconductor structure includes metallization structure, aplurality of conductive pads, and a dielectric layer. The plurality ofconductive pads is over the metallization structure. The dielectriclayer is on the metallization structure and covers the conductive pad.The dielectric layer includes a first dielectric film, a seconddielectric film, and a third dielectric film. The first dielectric filmis on the conductive pad. The second dielectric film is on the firstdielectric film. The third dielectric film is on the second dielectricfilm. The a refractive index of the first dielectric film is smallerthan a refractive index of the second dielectric film, and therefractive index of the second dielectric film is smaller than arefractive index of the third dielectric film.

The foregoing outlines structures of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for manufacturing a reflective structure, the method comprises: receiving a metallization structure; forming a first conductive pad, a second conductive pad, and a third conductive pad over the metallization structure; and forming a plurality of dielectric stacks over the metallization structure, the forming of the plurality of dielectric stacks comprising: forming a first dielectric stack over the first conductive pad; forming a second dielectric stack adjacent to the first dielectric stack, the second dielectric stack covers the second conductive pad; and forming a third dielectric stack adjacent to the second dielectric stack, the third dielectric stack covers the third conductive pad; wherein the thicknesses of the dielectric stacks are different.
 2. The method of claim 1, wherein forming each of the dielectric stacks comprises: forming a first dielectric film; forming a second dielectric film on the first dielectric film; and forming a third dielectric film on the second dielectric film.
 3. The method of claim 2, further comprising: forming a trench over an interval between each two adjacent dielectric stacks.
 4. The method of claim 3, wherein a bottom of each of the trenches is located at the first dielectric film.
 5. The method of claim 4, wherein a thickness of the first dielectric film below the bottom of the trench is smaller than about 50 angstroms.
 6. The method of claim 4, wherein a sidewall of each of the trenches comprises a side of the first dielectric film, a side of the second dielectric film, and a side of the third dielectric film.
 7. The method of claim 4, wherein the thicknesses of the first dielectric film, the second dielectric film, and the third dielectric film in each dielectric stack are different.
 8. The method of claim 1, further comprising: forming an electrical connection through each of the dielectric stacks; and forming a conductive oxide layer over each of the dielectric stacks and covers the electrical connection; wherein the electrical connection is in contact with the first conductive pad, the second conductive pad or the third conductive pad below the dielectric stacks.
 9. A method for manufacturing a reflective structure, the method comprises: receiving a metallization structure; forming a plurality of conductive pads over the metallization structure; forming a plurality of dielectric stacks over the conductive pads, respectively, wherein the thicknesses of the dielectric stacks are different; and isolating the dielectric stacks by forming a plurality of trenches over a plurality of intervals between each two adjacent dielectric stacks.
 10. The method of claim 9, wherein forming a plurality of dielectric stacks comprises: forming a first dielectric stack over a first conductive pad; forming a second dielectric stack over a second conductive pad, wherein the second dielectric stack is adjacent to the first dielectric stack; and forming a third dielectric stack over a third conductive pad, wherein the third dielectric stack is adjacent to the second dielectric stack.
 11. The method of claim 10, wherein forming the first dielectric stack comprises: forming a first dielectric film on the first conductive pad; forming a second dielectric film on the first dielectric film; and forming a third dielectric film on the second dielectric film.
 12. The method of claim 11, wherein a thickness of the first dielectric film is greater than a thickness of the second dielectric film, and the thickness of the second dielectric film is greater than a thickness of the third dielectric film.
 13. The method of claim 11, wherein forming the plurality of trenches comprises: etching a portion of the first dielectric stack and a portion of the second dielectric stack to exposing a side of the third dielectric film and a side of the second dielectric film.
 14. The method of claim 11, wherein a thickness of the first dielectric film below the bottom of the trench is smaller than about 50 angstroms.
 15. The method of claim 11, wherein a height of a first inner surface of the trench is different from a height of a second inner surface of the trench opposite to the first inner surface of the trench.
 16. A method for manufacturing a reflective structure, the method comprises: receiving a metallization structure; forming a plurality of conductive pads over the metallization structure; sequentially forming a plurality of dielectric stacks over the metallization structure, wherein the plurality of dielectric stacks covers the plurality of conductive pads, respectively, and the the thicknesses of the dielectric stacks are different; and forming a plurality of trenches over a plurality of intervals between each two adjacent dielectric stacks.
 17. The method of claim 16, wherein each dielectric stack comprises a plurality of dielectric films having a plurality of thicknesses altered in an ascending order from the dielectric film in proximity to a top of each dielectric stack to the dielectric film in proximity to a bottom of each dielectric stack.
 18. The method of claim 16, wherein each of the dielectric stacks comprises: a first dielectric film on one of the conductive pads; a second dielectric film on the first dielectric film; and a third dielectric film on the second dielectric film; wherein a refractive index of the first dielectric film is smaller than a refractive index of the second dielectric film, and the refractive index of the second dielectric film is smaller than a refractive index of the third dielectric film.
 19. The method of claim 16, further comprising: forming an electrical connection through each of the dielectric stacks; and forming a conductive oxide layer over each of the dielectric stacks and covers the electrical connection.
 20. The method of claim 19, further comprising: forming an insulating layer to fill the plurality of trenches; and depositing a micro-OLED over the insulating layer. 